A lone jogger runs across the promenade along the waterfront of Victoria harbour on the Kowloon side as the polluted skyline of Hong Kong island is visible in the background. Hong Kong's air pollution soared to record levels on March 22, the territory's Environmental Protection Department said, warning that a toxic stew enveloping the city was a danger to the public.

Hong Kong's air pollution soared to record levels Monday, the Environmental Protection Department said, warning that a toxic stew enveloping the city was a danger to the public.

The government agency said it found Air Pollution Index (API) readings that in several cases were more than double the level at which it advises the general public to stay indoors.

"Today's API is at record high levels," an agency spokeswoman said in an email to AFP.

Hong Kong's famed skyline and harbour is often shrouded in a blanket of haze which has been criticised as a public health disaster and blamed for driving some expatriates away from the international financial hub.

The API is a ratio based on the concentration of pollutants in the air, including sulfur dioxide and lead, with a higher reading indicating an increased danger to the public.

In July 2008, the city's environmental agency recorded air pollution levels as high as 202, well below Monday's record numbers which at midday ranged from a low of 192 to a record 453 reading at one roadside station.

Five other stations had readings above 400 at midday, the agency said.

"As the sandstorm from northern China is moving southward with the northeast monsoon and is now affecting Hong Kong, the Air Pollution Index is expected to reach the 'very high' or 'severe' level," it said in a statement.

People with heart or are advised to stay indoors at an API reading of more than 100. The public is advised to stay indoors or avoid prolonged exposure to areas at more than 200.

"This is very scary, over 300 is very scary, very polluted," Edwin Lau, director of Friends of the Earth Hong Kong, told AFP.

Lau said the city's pollution problem Monday was exacerbated by an unusual combination of sandstorms in China and strong southerly winds which are blowing particulates into Hong Kong.

"Hong Kong's air pollution is bad already, but this shows we're not dealing very well with the most severe weather situations. It is a very big alarm," he said.

Students at Hong Kong's Bradbury School were kept indoors Monday.

"We have stopped any outdoor physical activity or playing to safeguard the children," John Ainsworth, a vice-principal at the school, told AFP.

On March 5, a group of Hong Kong businesses -- including Starbucks, Pacific Coffee, Ben & Jerry's and Pure Fitness -- launched an unprecedented petition campaign to combat Hong Kong's worsening air pollution.

The organisers also placed ads in newspapers, warning that the city's smog "kills three people a day" and that its air is "three times dirtier than New York City's."

Data from the Hong Kong Observatory on March 2 showed that the annual number of hours of "reduced visibility" -- defined as visibility of less than eight kilometres (five miles) in the absence of fog, mist or rain -- skyrocketed to 1,139 last year from 295 in 1988.

Authorities often blame deteriorating air quality on emissions from the southern Chinese factory belt over Hong Kong's northern border.

But a study by the Civic Exchange think-tank last year said that Hong Kong's own road emissions were the dominant source of in the densely populated city of seven million.